1. Field of the Invention
The present invention relates to a method of manufacturing a color electroluminescent display apparatus applied to various types of thin-plate display apparatuses, and a method of bonding light-transmitting substrates used for the same.
2. Description of the Related Art
An electroluminescent (hereinafter, abbreviated as xe2x80x9cELxe2x80x9d) display apparatus is a thin display apparatus capable of matrix display like a liquid crystal display apparatus. The EL display apparatus comprises a plurality of EL devices arranged on a substrate. Each of the EL devices comprises an EL light emission layer interposed between a pair of electrodes, and acts as a picture element of the EL display apparatus. When a so-called high alternating field is generated between the pair of electrodes, the EL light emission layer causes electroluminescence, so that light is emitted from the EL light emission layer. This light is so-called EL light. That is, unlike the liquid crystal display apparatus, the EL display apparatus is of a self-light-emission-type display apparatus that is constituted only by solid-state devices. Moreover, compared to the liquid crystal display apparatus, the EL display apparatus is high in contrast and excellent in legibility. Since the EL display apparatus has the above-mentioned characteristics that cannot be obtained from the liquid crystal display apparatus, research thereon is being widely performed. In recent years, research has been performed on the achievement of a thin-film EL display apparatus capable of color display. The thin-film EL display apparatus, which is a type of the EL display apparatus, uses so-called thin-film EL devices as the EL devices.
The applicant has proposed a first prior art regarding the achievement of an EL display apparatus capable of color display in Japanese Examined Patent Publication JP-B2 3-77640 (1991). A color EL display apparatus using thin-film EL devices according to the first prior art has a structure such that three kinds of EL light emission layers that emit light beams of wavelengths of red, green and blue by electroluminescence, respectively, are arranged in parallel and the EL light emission layers are each sandwiched between a pair of electrodes. In order to put the color EL display apparatus to practical use, it is necessary for the EL light emission layers to emit light beams of the wavelengths with a brightness necessary for matrix display. Generally, the wavelength and the brightness of the light emitted from an EL light emission layer by electroluminescence depends on the material of the EL light emission layer. Since there are few materials that emit light beams of the wavelengths of red, green and blue with the above-mentioned brightness, it is difficult to realize the color EL display apparatus.
A second prior art regarding the achievement of a color EL display apparatus is disclosed in Japanese Unexamined Patent Publication JP-A 64-40887 (1989). The color EL display apparatus of this prior art includes a plurality of thin-film EL devices of a double insulation structure including a light emission layer that emits so-called white light by electroluminescence, and a plurality of organic color filters each transmitting light of the wavelength of only one of red, green and blue. The color filters are each placed directly on one electrode of the pair of electrodes of each thin-film EL device. The white light emitted from each EL device is divided into spectra by the color filters. Consequently, light beams of the wavelengths of red, blue and green exit from the color EL display apparatus.
The thin-film EL devices of the double insulation structure in which thin-film insulation layers are interposed between the electrodes and the light emission layers has a structure such that a multiplicity of thin film pieces are laminated. In forming the film pieces, a defect such as a pinhole is sometimes caused in the film pieces. In the case where the insulation layer has a defect such as a pinhole, when the high alternating field is created between the pair of electrodes of the thin-film EL devices, an electrical breakdown is caused at the pinhole and in the vicinity thereof, so that a microdischarge is caused. There are cases where the color filters on the electrodes deteriorates and breaks due to the microdischarge.
As a third prior art regarding the achievement of a color EL display apparatus, Japanese Unexamined Patent Publication JP-A 64-40888 (1989) discloses an art to prevent the above-mentioned deterioration and breakage of the color filters. FIG. 20 is an enlarged partial cross-sectional view of a color EL display apparatus 1 according to this prior art. The color EL display apparatus 1 comprises a main substrate 3, a light-transmitting substrate 4, a plurality of thin-film EL devices 5 of the double insulation structure, a plurality of color filters 6 and a sealing portion 7. The thin-film EL devices 5 are arranged on one surface 9 of the main substrate 3. The color filters 6 are arranged on one surface 10 of the light-transmitting substrate 4. The main substrate 3 and the light-transmitting substrate 4 are disposed so that the surfaces 9 and 10 are opposed with a predetermined gap in between. The sealing portion 7, which is so-called passivation protecting means, is disposed between the main substrate 3 and the light-transmitting substrate 4.
The method of manufacturing the color EL display apparatus 1 will briefly be described below. First, a plurality of lower electrodes 11 which are thin film strips are formed on the one surface 9 of the substrate 3. Then, a lower insulation layer 12, a light emission layer 13 and an upper insulation layer 14 are successively laminated in this order on all the lower electrodes 11. Then, a plurality of upper electrodes 15 which are thin film strips are formed on the upper insulation layer 14. The upper electrodes 15 each transmit light. The direction of length of the lower electrodes 11 and the direction of length of the upper electrodes 15 are perpendicular to each other when viewed from the direction of the normal 16 to the one surface 9 of the substrate 3. The portions where the lower electrodes 11 and the upper electrodes 15 intersect when viewed from the direction of the normal 16 are the thin-film EL devices 5. In order to improve the crystallinity of the light emission layer 13, after the light emission layer 13 is formed or after the upper insulation layer 14 is formed, annealing is performed in a vacuum or in an inert gas.
Then, the color filters 6 are formed on the one surface 10 of the light-transmitting substrate 4. Then, the substrate 3 and the light-transmitting substrate 4 are bonded by an epoxy resin 17 so that the surfaces 9 and 10 are opposed with the predetermined gap in between. Lastly, in order to form a protective material layer 18, the gap between the substrate 3 and the light-transmitting substrate 4 is filled with a gaseous or a liquid protective material. The epoxy resin 17 and the protective material layer 18 constitute the sealing portion 7. By the above-described process, the color EL display apparatus is completed.
Generally, the inactivation protecting means, that is, the sealing portion 7 is provided for shielding the thin-film EL devices from the atmosphere to thereby stabilize the thin-film EL devices and protecting the thin-film EL devices from mechanical failures. A so-called seal life which is one of the greatest characteristics of typical EL display apparatuses depends on the structure of the sealing portion.
A sealing portion currently used in a typical thin-film EL display apparatus is formed by use of a sealing substrate and a mixture liquid of silica gel and silicone oil. The process of forming the currently-used sealing portion will be described below. The typical thin-film EL display apparatus comprises a plurality of EL devices arranged on one surface of a substrate. First, a concave portion with a depth of 300 to 500 xcexcm is formed in one surface of the sealing substrate. Then, the sealing substrate and the substrate are bonded together so that the concave portion is opposed to the one surface of the substrate and that a filling hole is left. Then, the gap between the substrate and the sealing substrate is evacuated, and the mixture liquid is filled into the gap. Lastly, the filling hole is sealed, which completes the currently-used sealing portion.
The silica gel absorbs moisture intruding into the gap. The silicone oil circulates the silica gel in the gap and cools the EL devices. Consequently, the EL devices are protected from the influence of moisture and the like. The seal life obtained from the currently-used sealing portion is not less than 50 thousand hours.
In the color EL display apparatus 1 of the third prior art, the light-transmitting substrate 4 is used instead of the sealing substrate, and the protective material is filled into the gap between the substrate 3 and the light-transmitting substrate 4 to form the sealing portion 7. However, in the color EL display apparatus 1, in order to ensure a viewing angle sufficient for practical use, it is necessary that the gap between the substrate 3 and the light-transmitting substrate 4 be minimized. Consequently, the gap between the substrate 3 and the light-transmitting substrate 4 is frequently a fraction of the width of the gap in the currently-used sealing portion. Therefore, the seal life of the color EL display apparatus 1 is reduced to a fraction of that of the EL display apparatus having the currently-used sealing portion. Further, in the color EL display apparatus 1, since the silica gel enters the gap between the EL devices and the color filters, blur and distortion are caused in the display.
As a fourth prior art regarding the achievement of a color EL display apparatus, Japanese Unexamined Patent Publication JP-A 64-40888 (1989) further discloses an art to form color filters while employing the currently-used sealing portion. A color EL display apparatus according to the fourth prior art has a structure such that a plurality of EL devices are arranged on one surface of a substrate, a plurality of color filters are arranged on the other surface of the substrate and the above-described currently-used sealing portion is disposed on the one surface of the substrate. However, in the color EL display apparatus of the fourth prior art, since the thickness of the substrate is 1 to 2 mm, color displacements of the display are apt to be large and it is difficult to increase the degree of precision of the thin-film EL devices. Moreover, since the substrate thickness of the EL display apparatus is generally not less than 1.1 mm, the viewing angle of the color EL display apparatus of the fourth prior art is apt to be extremely narrow compared to those of the EL display apparatuses of the first to the third prior arts.
In order to improve the viewing angle of the color EL display apparatus of the fourth prior art, it is necessary that the thickness of the substrate be smaller than the thickness of general substrates. When the thickness of the substrate is reduced, in the steps of forming various thin films and the step of photoprocess in the process of manufacturing the color EL display apparatus of the fourth prior art, it is difficult to ensure a substrate strength necessary for the steps and to handle the substrate. At the same time, there is a possibility that the substrate cracks when the gap is evacuated in order to fill the mixture liquid into the gap. Because of these problems, it is difficult to reduce the thickness of the color EL display apparatus of the fourth prior art so as to be smaller than the thickness of general substrates.
Moreover, there are cases where a photo-setting resin is used, for example, for bonding a light-transmitting substrate having the color filters disposed thereon and the other substrate. However, since the color filters intercept light necessary for hardening the photo-setting resin such as ultraviolet rays, the photo-setting resin cannot harden in the area where the color filters are disposed.
Moreover, in the case where two light transmitting substrates are bonded together by filling the gap between the substrates with an adhesive, when there are portions where the adhesive is absent, that is, when bubbles are formed, the refractive index of the portions is different from that of the surrounding portions, so that the configurations of the bubbles appear on the display screen when a display is provided. This degrades the display quality.
In the case where two light-transmitting glass substrates are bonded together, a conventionally used method is such that an adhesive is thinly applied onto the surface of one glass substrate and then, the two substrates are brought into intimate contact with each other. However, in the case where an adhesive is applied, it cannot be helped that slight wavy patterns are formed on the surface. When the uneven portions of the wavy patterns are in contact with the substrate, air gaps are formed between the substrate and the adhesive. When there is no place for the air in the air gaps to escape into, the air gaps are left as bubbles.
As a method of bonding two substrates without such bubbles being formed, for example, Japanese Unexamined Patent Publication JP-A 63-18326 (1988) discloses a method in which bubbles are blown off by a spinner rotation after the substrates are bonded. Japanese Unexamined Patent Publication JP-A 9-278497 (1997) discloses a method in which when substrates are bonded together, the substrates are inclined by an apparatus for controlling the angles of the substrates in order that no bubbles are formed. Japanese Unexamined Patent Publication JP-A 3-126646 (1991) discloses a method in which when an adhesive is applied to the substrate, the thickness of the adhesive is controlled so as to monotonously increase from one end to the other end to thereby prevent the formation of bubbles when the substrates are bonded together. Japanese Unexamined Patent Publication JP-A 6-349962 (1994) discloses a bonding method in which a central portion of glass formed so that the central portion thereof is higher than the other portions thereof is melted to bond the two substrates to thereby prevent the formation of bubbles. However, the bonding methods disclosed in the prior arts all require separate apparatuses having complicated structures, which increases the manufacturing cost. Therefore, an easier method is desired in order to increase industrial use.
Moreover, when two substrates are bonded together by dropping a liquid hardening resin on one surface of a thin substrate, there are cases where the dropped resin concaves the thin substrate and the concaved portion is left as a distortion of the EL display screen to degrade the display quality.
Moreover, glass substrates generally have local and small asperities. FIG. 21 is a plan view schematically showing conditions in bonding substrates having such local concave portions. When the substrates are brought into intimate contact with each other so that a liquid hardening resin spreads between the substrates, as shown in FIG. 21, although the speed at which the resin spreads is constant in the area where a local concave portion P is absent, the resin spreading speed is lower in the local concave portion P than in the periphery. Consequently, as shown in FIG. 21, the resin spreads over the periphery of the concave portion P faster in the vicinity of the concave portion P, so that the periphery is filled with the resin without the resin being spread over the concave portion P. As a result, a bubble is left in the concave portion P.
An object of the invention is to provide a method of manufacturing a color EL display apparatus having a long seal life, a wide viewing angle and improved display quality, and a light-transmitting substrate bonding method used for the manufacturing method.
The invention provides a method of manufacturing a color EL display apparatus comprising the steps of:
forming a plurality of EL devices in which an EL light emission layer is interposed between a pair of electrodes, on one surface of a first light-transmitting substrate having a thickness larger than a predetermined reference thickness;
attaching a second substrate to the one surface of the first substrate with a predetermined gap in between;
filling a material for protecting the EL devices, into a gap between the one surface of the first substrate and the second substrate;
processing the first substrate so as to have the reference thickness; and
attaching color filters each capable of transmitting light of a predetermined wavelength to the other surface of the first substrate.
According to the invention, the light emitted from the EL display devices exits from the color EL display apparatus manufactured by the above-described method after being transmitted by the color filters. By the color filters being capable of transmitting light of different wavelengths, so-called multicolor light emission is enabled.
In the above-described manufacturing method, after the first substrate and the second substrate are bonded together and the material is filled into the gap between the substrates, the first substrate is processed so as to have the reference thickness. The reference thickness is, for example, smaller than that of the above-described prior art color EL apparatuses. Therefore, in the process of manufacturing the color EL display apparatus, the thickness of the first substrate is larger than the reference thickness during a period from the EL device forming process to the material filling process. Consequently, during the period, the strength of the first substrate is greater than that of a substrate of the reference thickness. Therefore, the first substrate is prevented from warping in the EL device forming process, and the handling of the first substrate in the forming process is facilitated. Further, the first substrate is prevented from cracking in the material filling process. Thus, the manufacture of the color EL display apparatus is easy compared to the case where the thickness of the first substrate is the reference thickness from the start of the manufacturing process.
Further, in the color EL display apparatus of the invention, the structure of the sealing portion comprising the second substrate and the material is substantially the same as the structure of the currently-used sealing portion of typical color EL display apparatuses. Therefore, the seal life of the color EL display apparatus of the invention is long compared to that of the color EL display apparatus of the above-described third prior art.
Consequently, a color EL display apparatus having a seal life sufficient for practical use can easily be manufactured.
Moreover, in the invention it is preferable that the reference thickness is not more than 1.2 times the width of an interval between one electrodes of the pairs of electrodes in two adjacent EL devices.
According to the invention, the reference thickness, that is, the after-processing thickness of the color EL display apparatus manufactured by the manufacturing method of the invention is not more than 1.2 times the width of the interval. Consequently, the viewing angle of the color EL display apparatus is not less than 160xc2x0. As a result, the viewing angle of the color EL display apparatus is sufficient for practical use.
Moreover, in the invention it is preferable that the reference thickness is not less than 25 xcexcm and not more than 200 xcexcm.
According to the invention, the reference thickness, that is, the after-processing thickness of the first substrate of the color EL display apparatus manufactured by the manufacturing method of the invention is not less than 25 xcexcm and not more than 200 xcexcm. This is for the following reason: At present, the electrode pitch of a prior art direct matrix color EL display apparatus featuring high-resolution display is not less than 2 per millimeter. Therefore, the distance between the electrodes of two adjacent EL devices in the prior art color EL display apparatus is approximately 50 to 150 xcexcm. Therefore, by the reference thickness being not more than 200 xcexcm, when the distance between the electrodes of adjacent EL devices in the color EL display apparatus manufactured by the manufacturing method of the invention is the same as that in the prior art color EL display apparatus, the viewing angle dependency of the color EL display apparatus is significantly improved compared to that of the prior art color EL display apparatus. The thinner the first substrate is, the higher the possibility is that the first substrate is damaged in the manufacturing process after the processing of the first substrate. Considering the processing accuracy of the first substrate, it is necessary to consider that there is an error of xc2x110 xcexcm in the after-processing thickness of the first substrate. From these, since there is no margin when the reference thickness is less than 25 xcexcm, the reference thickness is set to not less than 25 xcexcm.
Moreover, in the invention it is preferable that the reference thickness is not less than 50 xcexcm and not more than 100 xcexcm.
According to the invention, the reference thickness, that is, the after-processing thickness of the first substrate of the color EL display apparatus manufactured by the manufacturing method of the invention is not less than 50 xcexcm and not more than 100 xcexcm. This is for the following reason: In the case where the reference thickness is not more than 50 xcexcm, when the actual production of the color EL display apparatus is considered, it is difficult to ensure processing accuracy in the processing of the first substrate. Moreover, in this case, when the actual production of the color EL display apparatus is considered, handling of the first substrate is difficult after the processing of the first substrate. Therefore, the reference thickness is set to not less than 50 xcexcm in order to ensure the processing accuracy of the first substrate and to facilitate the handling of the first substrate. Moreover, considering the electrode pitch of currently-used EL panels, the reference thickness is set to not more than 100 xcexcm in order to obtain a viewing angle of 80xc2x0 at the electrode pitch. The viewing angle of 80xc2x0 is required when the color EL display apparatus is used as the display of a personal computer for private use.
Moreover, in the invention it is preferable that the second substrate has a thickness of 0.8 mm or more.
According to the invention, it is preferable that the thickness of the second substrate is not less than 0.8 mm. This is for the following reason: The second substrate not only forms a gap into which the material is filled but also suppresses the warp of the first substrate due to the internal stress in the EL devices during and after the processing of the first substrate. Moreover, a concave portion is frequently formed in the second substrate in order to maximize the gap into which the material is filled. Further, the second substrate is frequently made of a glass material. When the thickness of the second substrate is not less than 0.8 mm, the warp of the first substrate can surely be suppressed even when the second substrate is made of a glass material and has a concave portion formed therein.
Moreover, in the invention it is preferable that the method further comprises a step of attaching a third light-transmitting substrate to the other surface of the first substrate with the color filters in between.
According to the invention, in the color EL display apparatus manufacturing method, lastly, the third substrate is further attached to the other surface of the first substrate. Consequently, the color filters are protected by being sandwiched between the first substrate and the third substrate. Moreover, by further attaching the third substrate, the overall mechanical strength of the color EL display apparatus can be made greater than that in the case where the third substrate is not attached.
Moreover, in the invention it is preferable that the third substrate has a thickness of 0.5 mm or more.
According to the invention, the thickness of the third substrate is not less than 0.5 mm. This is for the following reason: Typically, a color EL display apparatus is frequently housed in a box together with a driving IC for driving the color EL display apparatus to form a so-called display unit. The display unit manufacturing process includes the step of connecting the tab of the driving IC to the electrodes of the EL devices and the step of placing the color EL display apparatus in the box. When the thickness of the third substrate is not less than 0.5 mm, the entire color EL display apparatus manufactured by the above-described manufacturing method can have a mechanical strength necessary for the display unit manufacturing process.
Consequently, the color EL display apparatus has a seal life sufficient for practical use and can easily be manufactured.
The invention provides a method of manufacturing a color EL display apparatus, comprising the steps of:
preparing EL devices in which a first light-transmitting electrode, an EL light emission layer and a second electrode are formed on one surface of a light-transmitting EL-device substrate and EL light is emitted from the other surface of the EL-device substrate, and a color filter substrate where color filters are disposed on one surface of a light-transmitting substrate; and
filling a thermosetting resin into a gap between the other surface of the EL-device substrate and the surface of the color filter substrate where the color filters are disposed, and then thermally setting the thermosetting resin to bond the color filter substrate and the EL-device substrate.
According to the invention, a thermosetting resin is filled into the gap between the other surface of the EL-device substrate and the surface of the color filter substrate where the color filters are disposed, and then, the substrates are heated to harden the thermosetting resin, thereby bonding the color filter substrate and the EL-device substrate. Conventionally, since a photo-setting resin is used for the bonding of the color filter substrate and the EL-device substrate, the photo-setting resin cannot be hardened in an area where the color filters are disposed. However, in the invention using a thermosetting resin, the color filter substrate and the EL-device substrate can be bonded by hardening the thermosetting resin by heating even in the area where the color filters are disposed. Consequently, the color filter substrate and the EL-device substrate can be bonded through an adhesive layer over the entire surface where the color filters are disposed, so that a sufficient bonding strength is obtained.
The invention provides a method of bonding two substrates at least one of which is a light-transmitting substrate, the method comprising the steps of dropping a liquid hardening resin on one substrate so as to convexly bulge; and
subsequently bring the two substrates into intimate contact so that the liquid hardening resin is spread to fill a gap between the substrates and be hardened.
According to the invention, the liquid hardening resin is dropped on one substrate so as to convexly bulge, that is, in a conical shape having one convex portion, and then, the two substrates are brought into intimate contact with the other substrate being pressed against the liquid hardening resin on the one substrate. At this time, since the liquid hardening resin convexly bulges, the liquid hardening resin and the other substrate are in contact at one point at the top of the portion of the dropped liquid hardening resin, and by bringing the substrates into intimate contact, the liquid hardening resin is radially spread from the top to fill the gap between the substrates. By the convex liquid hardening resin portion being thus spread, no air gap is formed in the resin, so that the resin can be filled in the gap between the substrates with the formation of bubbles being prevented. The two substrates can be bonded by hardening the liquid hardening resin after the resin is filled. By such an easy method, the substrates can be bonded without any bubbles being mixed, so that the manufacturing cost can be reduced.
The invention provides a method of bonding two substrates at least one of which is a light-transmitting substrate, comprising the steps of:
dropping a liquid hardening resin onto each of the two substrates so as to convexly bulge; and
subsequently bring the two substrates into intimate contact so that tops of resin portions on the substrates are in contact with each other and the liquid hardening resin is spread to fill a gap between the substrates and is hardened.
According to the invention, when the two substrates are brought into intimate contact with each other so that the tops of the portions of the liquid hardening resin dropped on the two substrates so as to convexly bulge are in contact with each other, the substrates are connected at one resin portion, so that when the substrates are brought into intimate contact, the liquid hardening resin is radially spread from one resin portion and the resin is filled in the gap between the substrates without any bubbles being formed. By thus dropping the liquid hardening resin onto both substrates, compared to the case where the liquid hardening resin is dropped onto only one substrate, the portion of the substrate with which the dropped resin is in contact is small even when the amount of application is the same, so that the resin can be filled in the gap between the substrates with the mixture of bubbles being further prevented. Moreover, the manufacturing cost can be reduced by such an easy bonding method.
The invention provides a method of bonding two substrates at least one of which is a light-transmitting substrate, comprising the steps of:
dropping a liquid hardening resin onto one substrate at a plurality of points along a straight line or a zigzag line; and
subsequently bringing the two substrates into intimate contact so that the liquid hardening resin is spread to fill a gap between the substrates and is hardened.
According to the invention, the two substrates are brought into intimate contact after the liquid hardening resin is dropped at a plurality of points along a straight line or a zigzag line, so that the liquid hardening resin can effectively be spread over the entire substrate even when the substrate is rectangular. Moreover, in the invention, although the liquid hardening resin is dropped at a plurality of points, since the liquid hardening resin portions are arranged along a straight line or a zigzag line, a gap is prevented from being left between the resin portions when the resin is spread. Consequently, the formation of bubbles is prevented and the resin can substantially uniformly be applied over the entire surface even when the substrate is rectangular. Moreover, the manufacturing cost can be reduced by such an easy bonding method.
In the invention it is preferable that when being heated, the liquid hardening resin has a viscosity lower than that at an ordinary temperature, and
that a force is exerted on the substrates so that the resin between the substrates is spread while the substrates are being heated.
According to the invention, by heating the two substrates when the substrates are brought into intimate contact, the viscosity of the liquid hardening resin decreases, so that the substrates can be brought into intimate contact with the resin being thinly and uniformly spread between the substrates. Since the viscosity is high when the resin is dropped, the resin can suitably be dropped so as to convex. In the case where the viscosity is low when the resin is dropped, since the resin thinly spreads over the substrates, an air gap is formed when the substrates are brought into intimate contact, so that bubbles are formed. In the invention, however, by dropping the resin in a high viscosity condition, the resin can suitably be dropped so as to convex in a conical shape, so that the resin can be spread without any bubbles being formed. Moreover, by exerting a force on the substrates while heating the substrates, the resin can thinly be filled in the gap between the substrates.
In the invention it is preferable that when the EL-device substrate and the color filter substrate are bonded together, a liquid thermosetting resin is dropped on one substrate so as to convexly bulge, the two substrates are brought into intimate contact so that the thermosetting resin is spread to fill the gap between the substrates, the substrates are fixed by a photo-setting resin at a portion where color filters are not disposed under a condition where the EL-device substrate and the color filter substrate are positioned, and then, the substrates are heated to harden the thermosetting resin, thereby bonding the two substrates.
According to the invention, by bringing the two substrates into intimate contact after the liquid thermosetting resin is dropped onto one substrate so as to convex, the liquid thermosetting resin can be filled in the gap between the substrates without any bubbles being formed. The photo-setting resin is applied onto the portion between the substrates where the color filters are not disposed, and after the EL-device substrate and the color filter substrate are positioned by aligning the electrode pattern of the EL devices and the color filter pattern of the color filter substrate, the photo-setting resin is hardened by applying light, thereby temporarily fixing the EL-device substrate and the color filter substrate. Then, the thermosetting resin is hardened by heating, so that the substrates are bonded. Thus, since the resin can thermally be hardened after the substrates are positioned at an ordinary temperature and temporarily fixed, a problem is eliminated such that it is necessary to position the substrates while hardening the resin by heating.
In the invention it is preferable that when the EL-device substrate and the color filter substrate are bonded together, a thermosetting resin is dropped onto each of the substrates so as to convexly bulge, the two substrates are brought into intimate contact so that tops of resin portions on the substrates are in contact with each other to thereby spread the thermosetting resin to fill the gap between the substrates, the substrates are fixed by a photo-setting resin at a portion where the color filters are not disposed under a condition where the EL-device substrate and the color filter substrate are positioned, and then, the substrates are heated to harden the thermosetting resin, thereby bonding the substrates.
According to the invention, by bringing the two substrates into intimate contact so that the tops of the portions of the liquid thermosetting resin dropped on the EL-device substrate and the color filter substrate so as to convex are in contact, the resin can be filled in the gap between the substrates with the mixture of bubbles being more surely prevented. Moreover, since the color filter substrate and the EL-device substrate are temporarily fixed by the photo-setting resin under a condition where the two substrates are positioned at an ordinary temperature, it is unnecessary to perform positioning when the resin is thermally hardened.
In the invention it is preferable that when the EL-device substrate and the color filter substrate are bonded together, a thermosetting resin is dropped so as to convexly bulge on one substrate at a plurality of points along a straight line or a zigzag line, the two substrates are brought into intimate contact to spread the thermosetting resin so as to fill a gap between the substrates, the substrates are fixed by a photo-setting resin at a portion where the color filters are not disposed under a condition where the EL-device substrate and the color filter substrate are positioned, and then, the substrates are heated to harden the thermosetting resin, thereby bonding the substrates.
According to the invention, since the liquid thermosetting resin is dropped on one substrate at a plurality of points along a straight line or a zigzag line, the liquid thermosetting resin can effectively and uniformly be filled in the gap between the two substrates without any bubbles being formed even when the substrates are rectangular. Moreover, since the color filter substrate and the EL-device substrate are temporarily fixed by the photo-setting resin at an ordinary temperature in a condition where the substrates are positioned, it is unnecessary to perform positioning when the resin is thermally hardened.
In the invention it is preferable that the liquid thermosetting resin is lower in viscosity when heated than at an ordinary temperature, and
that when the substrates are heated, a force is exerted on the substrates so that the resin between the substrates is spread.
According to the invention, when the resin is dropped onto the substrate at an ordinary temperature, since the viscosity is high, the resin can suitably be dropped so as to convexly bulge. Since the viscosity of the liquid hardening resin decreases when the substrates are heated, the resin is thinly and uniformly spread to fill the gap between the substrates, and when the substrates are further heated to the hardening point, the liquid thermosetting resin is hardened, so that the color filter substrate and the EL-device substrate are bonded. Thus, since the thickness of the adhesive layer is decreased, the viewing angle deterioration due to color displacements can be prevented.
The invention provides a method of bonding two substrates at least one of which is a light-transmitting substrate, comprising the steps of:
dropping a liquid hardening resin on a surface of one substrate so as to convexly bulge;
directing the surface where the resin is dropped, downward so as to face a surface of the other substrate; and
bonding the substrates to each other so that the resin is spread to fill a gap between the substrates and is hardened.
According to the invention, since the liquid hardening resin is dropped onto only one surface, the manufacturing cost can be reduced, and since the substrates are bonded together with the resin dropped surface facing downward, even a low-viscosity resin can convexly be bulged effectively to bond the substrates together. Consequently, a low-viscosity resin can be used, the substrates are not distorted even when the substrates are thin, and the substrates can be bonded by thinly and uniformly spreading the resin between the substrates without any bubbles being formed.
The invention provides a method of bonding two substrates at least one of which is a light-transmitting substrate, comprising the steps of:
interposing a liquid hardening resin between the substrates;
spreading the liquid hardening resin between the substrates by use of a capillary phenomenon of the resin; and
hardening the resin thereafter.
According to the invention, the liquid hardening resin is spread to fill the gap between the substrates by the capillary phenomenon. That is, since the gap between the substrates is extremely small, when the liquid hardening resin is interposed between the substrates, the resin spreads over the entire surfaces of the substrates by the capillary phenomenon due to the surface tension of the resin. Since the surface tension causes a force to act in a direction that brings the substrates into intimate contact, a force is exerted in the direction that brings the two substrates into intimate contact with each other without an external force being exerted on the substrates. When the resin is dropped onto the surface of the substrate and the two substrates are bonded together, the resin dropped portion concaves when the substrate is thin. However, since resin is discharged from the concaved resin dropped portion in the process of spread of the resin to the periphery due to the capillary phenomenon, the concave is reduced at the resin dropped portion, so that the substrate becomes flat. As the method of interposing the resin between the substrates, a method in which the resin is dropped onto the peripheries of two substrates being in intimate contact and the resin is spread between the substrates can be used in addition to the method in which the resin is dropped on the surface of the substrate and the substrates are bonded together.
In the invention it is preferable that the liquid hardening resin is a thermosetting resin, and a viscosity of the resin at an ordinary temperature is higher than that of the resin thermally hardened.
According to the invention, by using a thermosetting resin whose viscosity at an ordinary temperature is higher than that of the thermally hardened resin, the viscosity is high when the resin is dropped, so that the resin can effectively be dropped so as to convexly bulge. When the two substrates are bonded together under this condition and heated, the viscosity of the resin between the substrates decreases, so that the resin is thinly spread between the substrates. When the substrates are further heated to the hardening temperature, the substrates can be bonded with the resin being thermally hardened in a thinly spread condition. Thus, the substrates can be bonded by thinly spreading the resin between the substrates with the mixture of bubbles being surely prevented.
In the invention it is preferable that a spacer of a predetermined grain diameter is interposed between the substrates.
According to the invention, since the spacer of the predetermined grain diameter is interposed between the substrates, a predetermined distance can be maintained between the substrates. When the resin between the substrates spreads, a force acts by the surface tension in a direction that brings the substrates into intimate contact as mentioned above. However, when the substrates are in absolute contact, the resin is prevented from spreading. On the contrary, according to the invention, the substrates are prevented from being in absolute contact by interposing the spacer between the substrates, so that the resin can smoothly be spread between the substrates.
In the invention it is preferable that the spacer is fixed to the surface of one substrate in advance, and the substrates are bonded together thereafter.
According to the invention, since the spacer is fixed to the surface of one substrate in advance and the substrates are bonded together thereafter, the productivity is excellent. Moreover, since the spacer is fixed in advance, the spacer can be prevented from dropping when the substrates are bonded together.
In the invention it is preferable that the grain diameter of the spacer is not less than 10 xcexcm.
According to the invention, the grain diameter of the spacer is not less than 10 xcexcm. When there is a local concave portion in the surface of the substrate and the difference between the substrate-to-substrate distance at the concave portion and the substrate-to-substrate distance at the periphery thereof is large, the speed of spread of the resin is different between at the local concave portion and at the periphery, so that a bubble is left in the local concave portion. In the invention, by interposing the spacer with a grain diameter of not less than 10 xcexcm, the difference in substrate-to-substrate distance between at the local concave portion and at the periphery thereof can be reduced, so that the resin substantially uniformly spreads. As a result, the formation of bubbles can be surely prevented.
In the invention it is preferable that when an area of a range between the substrates to be filled with the resin is S and the grain diameter of the spacer is d, an amount D of the liquid hardening resin inserted between the substrates is selected so as to fall within the following range:
Sxc2x7d less than D less than Sxc2x7(d+12 xcexcm).
According to the invention, the amount of the dropped resin is selected so as to fall within the above-mentioned range. When the amount of the dropped resin is too large, the resin is filled in the entire gap between the substrates before the resin is sufficiently discharged from the resin dropped portion, so that the spread of the resin due to the capillary phenomenon stops. Then, excessive resin is left in the resin dropped portion and causes a distortion in the substrate as a concave. When the amount of the dropped resin is too small, the resin cannot completely be filled in the gap to be filled with the resin. Therefore, it is necessary that an appropriate amount of resin be filled between the substrates. Since the substrate-to-substrate distance is maintained constant by interposing the spacer between the substrates, ideally, the amount D of the resin inserted between the substrates is:
D=Sxc2x7d. 
When the resin of the amount satisfying the expression is inserted between the substrates, an appropriate amount of resin is filled in the gap between the substrates, so that no concave is caused in the resin dropped portion and no bubbles are formed. However, since there are local asperities on the surfaces of the substrates in actuality, it is necessary that the amount of the dropped and inserted resin vary. As a result of an examination, the inventor found that when the amount satisfies the following condition, only a distortion that becomes no problem is caused although the amount is larger than the ideal amount:
D less than Sxc2x7(d+12 xcexcm). 
Moreover, to fill the range between the substrates to be filled with the resin, the resin of an amount larger than the ideal amount is necessary. Therefore, it is necessary that the amount D of the resin to be inserted satisfy the following condition:
Sxc2x7d less than D. 
In the invention it is preferable that one of the two substrates is a light-transmitting EL-device substrate, the El device substrate, having a first light-transmitting electrode, an EL light emission layer and a second electrode formed on one surface thereof, and emitting EL light from the other surface; and
that the other substrate of the two substrates is a light-transmitting color filter substrate and has color filters disposed on one surface thereof.
According to the invention, by bonding the EL-device substrate and the color filter substrate by the above-described substrate bonding methods, an EL display apparatus can be manufactured in which the distortion of the substrates and the formation of bubbles are prevented and the display quality is not deteriorated.